Re: [Haskell-cafe] WriterT [w] IO is not lazy in reading [w]

2008/12/31 Paolino :

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I must ask why runWriterT k :: State s (a,[Int]) is working. Looks like I could runIO the same way I evalState there. In that case I wouldn't wait for the State s action to finish.

Thanks

Assuming you have Control.Monad.State.Lazy (which I think is the default), here is the difference: [...] There's a much simpler way of understanding why you must wait for an IO computation to finish before you can use the result. In IO you can

On Thu, 2009-01-01 at 02:17 -0800, Ryan Ingram wrote: throw exceptions (IOErrors), so you must wait until an IO computation is finished to know that there is any result at all.